Avelo diving system

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The Avelo diving system is a single cylinder, back-mounted scuba set with variable density buoyancy control. The gas cylinder is a carbon fibre over aluminium liner filament wound pressure vessel with a charging pressure of 300 bar and a gas capacity of about 106 cubic feet of atmospheric pressure air or recreational nitrox. The fully charged set is slightly buoyant and lighter than the equivalent scuba set using a metal cylinder and inflatable buoyancy compensator. Buoyancy of the set is adjustable by injecting ambient water into the cylinder to increase density and releasing it to reduce density. Less ballast weight is needed by the diver. [1] [2] [3]

Contents

Purpose

The system was developed by engineer and diving instructor Aviad Cahana as a way to reduce the mass of recreational scuba equipment, as an ergonomic improvement, and to reduce the task loading and risk in buoyancy control. Poor buoyancy control and loss of buoyancy control have been implicated in a significant proportion of fatal scuba diving incidents. [3]

Operating principle

A buoyancy compensator (BC) works by adjusting the average density of the diver and their attached equipment to be greater than, equal to, or less than the density of the diving medium. [4] This can be done in either of two ways:

As of 2021, the overwhelming majority of BCs are variable volume types, inflated by gas at ambient pressure, but the variable density type is used in the Avelo diving system. [5] [6]

Components

The Avelo system comprises two major components, which are firmly connected together when in use. The manufacturers call them the "hydrotank" and "jetpack". A conventional two-stage open circuit scuba regulator with gas pressure monitoring is also needed to deliver the gas to the diver at ambient pressure on demand. [5] [6] Dry weight of the system is 36 pounds (16 kg) [3]

"Hydrotank"

The Avelo system eliminates the conventional variable volume buoyancy compensator bladder in favour of a variable density buoyancy compensator in the form of a constant volume breathing gas storage container referred to as the "hydrotank" which is a high pressure, carbon fibre wound composite pressure vessel on an aluminium liner which contains a tough flexible bladder to separate the stored breathing gas from the ballast water, both of which are carried in the hydrotank. Gas charging pressure is about 300bar, and the safe working pressure is considerably higher. The tanks are tested to 16,000 pounds per square inch (1,100 bar). The top end of the hydrotank has a 300 bar rated DIN scuba cylinder valve for regulator attachment, and the internal bladder is connected to this inside the cylinder so that the breathing gas is stored inside the bladder, which is constrained by the cylinder walls, so that it is not under high stress when under pressure. Water can be injected into the hydrotank on the outside of the badder through a fitting at the bottom end of the cylinder by a high pressure pump to increase the mass, and thereby the average density of the hydrotank. Since the bladder is elastic, the pressure of the water in the hydrotank is effectively the same as the gas pressure. [5] [6] [3]

The hydrotank is a relatively long, narrow hemispherical ended cylinder, which is an efficient form factor for keeping the mass low. There are two sizes. The standard 10 litre hydrotank contains approximately 106 cubic feet of breathing gas by American measure at 300 bars (4,400 psi) and the smaller 8 litre version is shorter to better accommodate smaller divers, and will contain 80% of the free gas content at the same pressure as the larger tank. [5] [6] [3] [1]

"Jetpack"

The "jetpack" refers to the backplate, harness, high-pressure water pump and battery pack assembly used to carry the hydrotank and operate the buoyancy control by adding ambient water to the interior of the hydrotank to decrease it's buoyancy, and release the water back to the surroundings to increase buoyancy after return to the surface. [5] [3]

The pump is a high pressure positive displacement pump with a low delivery volume, capable of producing enough pressure to inject water into the hydrotank against the internal gas pressure. When the pump stops, the water does not flow back through it, and must be manually released by a bypass valve. The system is protected from overpressurisation by an pressure relief valve. [5] [6] [3]

Power for the pump is provided from a rechargeable battery pack. This can be swapped out at the dive site for a fully charged pack between dives, and is usually sufficient for a day's worth of dives. When switched on the pump will run for a limited time before automatically switching off, or can be switched off manually. [5] [6] [3]

Diver weighting

Since the buoyancy is controlled by reducing buoyancy of the diver system using ambient water, less ballast weight is required. In some cases, with a low volume diving suit, the diver may not require any additional ballast. [3]

There are places on the hydrotank and jetpack where weights can be secured if necessary, a weight belt can be worn, or weight pockets can be fitted to the harness straps for ditchable weights or trim weights. [3]

Operational procedure

The system starts the dive at nominal charging pressure and slightly positive buoyancy, with no water in the cylinder. The diver is positively buoyant at this stage, and activates the pump to add water ballast to the cylinder until neutral or slightly negative, allowing descent by finning downward. During descent a wetsuit will compress, reducing buoyancy by the volume reduction of the suit, and a dry suit will also compress. The diver will compensate for dry suit compression in the usual way by minimal inflation to avoid suit squeeze. There should be no need to adjust water ballast during descent. [6] [3] [5]

At depth, the diver should still be approximately neutral, or slightly negative, to an extent where control of lung volume can comfortably compensate. Dive depth variations should not affect buoyancy sufficiently for depth of breathing to not comfortably compensate. As the dive progresses and gas is used up, the diver will become slightly lighter, and when it is noticeable that depth of breathing is no longer comfortably compensating, an addition of water to the cylinder will be done to correct the buoyancy, and this may be sufficient for the rest of the dive. A second adjustment may be desirable near the end of the dive. Ascent is by swimming upwards at neutral buoyancy. Dry suit buoyancy will be controlled in the standard way by allowing the expanding gas to escape through the shoulder dump valve. Wet suit buoyancy may not change sufficiently to require action, or may need a small water addition at the safety stop. [6] [3] [5]

On surfacing, the diver will manually dump the water in the cylinder to achieve maximum positive buoyancy, and reduce the weight of the equipment to facilitate exit from the water. [6] [3] [5]

Amount of water used for ballast

The total mass of air or nitrox that can be filled into the standard 10 litre cylinder is approximately 10/1000m3 x 300 x 1.2kg/m3 = 3.6kg. This is the theoretical maximum buoyancy change that might need compensation during a dive, if the diver uses up all the available gas. If the diver is about 2kg positive before the dive, an additional 2kg would have to be added to the cylinder to achieve neutral buoyancy at the start of descent, and this added to 3.6kg is 5.6kg, a bit more than half the volume of the cylinder. This can be considered an extreme situation. [7] The implication is that a reasonable amount of bailout or decompression gas carried in a sling cylinder can be compensated by the remaining cylinder volume. Although the Avelo system is currently marketed as recreational, no decompression stops diving equipment, it remains possible for a contingency to cause the diver to use up or lose all the gas, or need to share with a buddy, and divers who choose to carry bailout can do so within the capabilities of the equipment.

Safety

The Avelo system was developed with the intention of improving scuba safety in two ways. Firstly it reduces the mass of the equipment that must be carried by the diver out of the water, which is an ergonomic improvement that reduces the risk of injury due to carrying heavy weights. It also reduces task loading relating to buoyancy control throughout the dive, allowing the diver to concentrate on other matters, and facilitating safer and more controlled ascents and descents, particularly by less skilled divers. In this way it indirectly reduces the risk of barotrauma and decompression illness due to uncontrolled ascents and descents. [3]

Failure modes

Maintenance

Maintenance is similar to that recommended for other open circuit scuba equipment. The pump must be run in fresh water to rinse the interior after a dive, but the cylinder does not need to be rinsed inside. The cylinder requires hydrostatic testing and visual inspection as for other diving cylinders, the bladder must be replaced every five years or if it fails an inspection, and the battery pack must be rinsed in fresh water and recharged after use. The harness and cylinder should be washed down with fresh water after use as for other scuba sets. [2]

Monitoring the breathing gas

Gas pressure can be monitored during the dive using a standard analog submersible pressure gauge or an air-integrated dive computer, in the same way that it would be monitored for a regular scuba set. There is an increase in pressure at the start of the dive when water is injected to achieve neutral buoyancy, and that peak pressure is used as the reference pressure for rule of thirds or other gas use strategies. The volume of gas in the cylinder will decrease slightly when water is injected, along with the pressure increase, and this should be taken into account. It is usually a small proportion of the initial volume. [3]

Training and certification

A one-day, two-dive Recreational Avelo Diver (RAD) specialty course is required before divers can use or rent the equipment independently. This is mainly to familiarise the diver with the equipment and the different approach to buoyancy control that is necessary. [2] [3] [1]

Availability and price

As of October 2024, the units are only available for rental at specific dive centres. This is expected to change depending on market penetration. [2] [3]

Related Research Articles

<span class="mw-page-title-main">Scuba set</span> Self-contained underwater breathing apparatus

A scuba set, originally just scuba, is any breathing apparatus that is entirely carried by an underwater diver and provides the diver with breathing gas at the ambient pressure. Scuba is an anacronym for self-contained underwater breathing apparatus. Although strictly speaking the scuba set is only the diving equipment that is required for providing breathing gas to the diver, general usage includes the harness or rigging by which it is carried and those accessories which are integral parts of the harness and breathing apparatus assembly, such as a jacket or wing style buoyancy compensator and instruments mounted in a combined housing with the pressure gauge. In the looser sense, scuba set has been used to refer to all the diving equipment used by the scuba diver, though this would more commonly and accurately be termed scuba equipment or scuba gear. Scuba is overwhelmingly the most common underwater breathing system used by recreational divers and is also used in professional diving when it provides advantages, usually of mobility and range, over surface-supplied diving systems and is allowed by the relevant legislation and code of practice.

<span class="mw-page-title-main">Diving cylinder</span> Container to supply high pressure breathing gas for divers

A diving cylinder or diving gas cylinder is a gas cylinder used to store and transport high pressure gas used in diving operations. This may be breathing gas used with a scuba set, in which case the cylinder may also be referred to as a scuba cylinder, scuba tank or diving tank. When used for an emergency gas supply for surface supplied diving or scuba, it may be referred to as a bailout cylinder or bailout bottle. It may also be used for surface-supplied diving or as decompression gas. A diving cylinder may also be used to supply inflation gas for a dry suit or buoyancy compensator. Cylinders provide gas to the diver through the demand valve of a diving regulator or the breathing loop of a diving re-breather.

<span class="mw-page-title-main">Buoyancy compensator (diving)</span> Equipment for controlling the buoyancy of a diver

A buoyancy compensator (BC), also called a buoyancy control device (BCD), stabilizer, stabilisor, stab jacket, wing or adjustable buoyancy life jacket (ABLJ), depending on design, is a type of diving equipment which is worn by divers to establish neutral buoyancy underwater and positive buoyancy at the surface, when needed.

<span class="mw-page-title-main">Diving weighting system</span> Ballast carried to counteract buoyancy

A diving weighting system is ballast weight added to a diver or diving equipment to counteract excess buoyancy. They may be used by divers or on equipment such as diving bells, submersibles or camera housings.

<span class="mw-page-title-main">Backplate and wing</span> Type of back-mount scuba harness

A backplate and wing is a type of scuba harness with an attached buoyancy compensation device (BCD) which can be used to establish neutral buoyancy underwater and positive buoyancy at the surface. Unlike most other BCDs, the backplate and wing is a modular system, in that it consists of separable components. The core components of this system are:

<span class="mw-page-title-main">Scuba diving</span> Swimming underwater, breathing gas carried by the diver

Scuba diving is a mode of underwater diving whereby divers use breathing equipment that is completely independent of a surface breathing gas supply, and therefore has a limited but variable endurance. The name scuba is an acronym for "Self-Contained Underwater Breathing Apparatus" and was coined by Christian J. Lambertsen in a patent submitted in 1952. Scuba divers carry their own source of breathing gas, usually compressed air, affording them greater independence and movement than surface-supplied divers, and more time underwater than free divers. Although the use of compressed air is common, a gas blend with a higher oxygen content, known as enriched air or nitrox, has become popular due to the reduced nitrogen intake during long or repetitive dives. Also, breathing gas diluted with helium may be used to reduce the effects of nitrogen narcosis during deeper dives.

<span class="mw-page-title-main">Neutral buoyancy</span> Equilibrium between buoyancy and weight of an immersed object

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<span class="mw-page-title-main">Ascending and descending (diving)</span> Procedures for safe ascent and descent in underwater diving

In underwater diving, ascending and descending is done using strict protocols to avoid problems caused by the changes in ambient pressure and the hazards of obstacles near the surface such as collision with vessels. Diver certification and accreditation organisations place importance on these protocols early in their diver training programmes. Ascent and descent are historically the times when divers are injured most often when failing to follow appropriate procedure.

<span class="mw-page-title-main">Scuba gas planning</span> Estimation of breathing gas mixtures and quantities required for a planned dive profile

Scuba gas planning is the aspect of dive planning and of gas management which deals with the calculation or estimation of the amounts and mixtures of gases to be used for a planned dive. It may assume that the dive profile, including decompression, is known, but the process may be iterative, involving changes to the dive profile as a consequence of the gas requirement calculation, or changes to the gas mixtures chosen. Use of calculated reserves based on planned dive profile and estimated gas consumption rates rather than an arbitrary pressure is sometimes referred to as rock bottom gas management. The purpose of gas planning is to ensure that for all reasonably foreseeable contingencies, the divers of a team have sufficient breathing gas to safely return to a place where more breathing gas is available. In almost all cases this will be the surface.

<span class="mw-page-title-main">Emergency ascent</span> An ascent to the surface by a diver in an emergency

An emergency ascent is an ascent to the surface by a diver in an emergency. More specifically, it refers to any of several procedures for reaching the surface in the event of an out-of-gas emergency, generally while scuba diving.

<span class="mw-page-title-main">Diver trim</span> Balance and orientation skills of an underwater diver

The trim of a diver is the orientation of the body in the water, determined by posture and the distribution of weight and volume along the body and equipment, as well as by any other forces acting on the diver. Both static trim and its stability affect the convenience and safety of the diver while under water and at the surface. Midwater trim is usually considered at approximately neutral buoyancy for a swimming scuba diver, and neutral buoyancy is necessary for efficient maneuvering at constant depth, but surface trim may be at significant positive buoyancy to keep the head above water.

<span class="mw-page-title-main">Scuba skills</span> The skills required to dive safely using a self-contained underwater breathing apparatus.

Scuba skills are skills required to dive safely using self-contained underwater breathing apparatus, known as a scuba set. Most of these skills are relevant to both open-circuit scuba and rebreather scuba, and many also apply to surface-supplied diving. Some scuba skills, which are critical to divers' safety, may require more practice than standard recreational training provides to achieve reliable competence.

Diving hazards are the agents or situations that pose a threat to the underwater diver or their equipment. Divers operate in an environment for which the human body is not well suited. They face special physical and health risks when they go underwater or use high pressure breathing gas. The consequences of diving incidents range from merely annoying to rapidly fatal, and the result often depends on the equipment, skill, response and fitness of the diver and diving team. The classes of hazards include the aquatic environment, the use of breathing equipment in an underwater environment, exposure to a pressurised environment and pressure changes, particularly pressure changes during descent and ascent, and breathing gases at high ambient pressure. Diving equipment other than breathing apparatus is usually reliable, but has been known to fail, and loss of buoyancy control or thermal protection can be a major burden which may lead to more serious problems. There are also hazards of the specific diving environment, and hazards related to access to and egress from the water, which vary from place to place, and may also vary with time. Hazards inherent in the diver include pre-existing physiological and psychological conditions and the personal behaviour and competence of the individual. For those pursuing other activities while diving, there are additional hazards of task loading, of the dive task and of special equipment associated with the task.

Investigation of diving accidents includes investigations into the causes of reportable incidents in professional diving and recreational diving accidents, usually when there is a fatality or litigation for gross negligence.

Diving procedures are standardised methods of doing things that are commonly useful while diving that are known to work effectively and acceptably safely. Due to the inherent risks of the environment and the necessity to operate the equipment correctly, both under normal conditions and during incidents where failure to respond appropriately and quickly can have fatal consequences, a set of standard procedures are used in preparation of the equipment, preparation to dive, during the dive if all goes according to plan, after the dive, and in the event of a reasonably foreseeable contingency. Standard procedures are not necessarily the only courses of action that produce a satisfactory outcome, but they are generally those procedures that experiment and experience show to work well and reliably in response to given circumstances. All formal diver training is based on the learning of standard skills and procedures, and in many cases the over-learning of the skills until the procedures can be performed without hesitation even when distracting circumstances exist. Where reasonably practicable, checklists may be used to ensure that preparatory and maintenance procedures are carried out in the correct sequence and that no steps are inadvertently omitted.

<span class="mw-page-title-main">Human factors in diving equipment design</span> Influence of the interaction between the user and the equipment on design

Human factors in diving equipment design are the influences of the interactions between the user and equipment in the design of diving equipment and diving support equipment. The underwater diver relies on various items of diving and support equipment to stay alive, healthy and reasonably comfortable and to perform planned tasks during a dive.

A variable-buoyancy pressure vessel system is a type of rigid buoyancy control device for diving systems that retains a constant volume and varies its density by changing the weight (mass) of the contents, either by moving the ambient fluid into and out of a rigid pressure vessel, or by moving a stored liquid between internal and external variable-volume containers. A pressure vessel is used to withstand the hydrostatic pressure of the underwater environment. A variable-buoyancy pressure vessel can have an internal pressure greater or less than ambient pressure, and the pressure difference can vary from positive to negative within the operational depth range, or remain either positive or negative throughout the pressure range, depending on design choices.

References

  1. 1 2 3 4 Wood, Craig; Davison, Ben (March 2024). "Diving the Avelo System". www.undercurrent.org. Retrieved 4 October 2024.
  2. 1 2 3 4 5 "Avelo is here. This changes everything!". DiversReady. 29 May 2023. Retrieved 4 October 2024– via TouTube.
  3. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Kurtis, Ken (15 March 2023). "Zoom Seekers: Aviad Cahana & Dan Orr - The Avelo System (March 14, 2023)" . Retrieved 4 October 2024– via YouTube.
  4. 1 2 Raymond, Kieth A; West, Brian; Cooper, Jeffrey S. (January 2021). Diving Buoyancy. Updated 2021 Jun 29. Treasure Island, FL.: StatPearls Publishing. PMID   29261960. Archived from the original on 2024-03-19. Retrieved 2021-12-29– via StatPearls [Internet]. CC-by-sa-4.0
  5. 1 2 3 4 5 6 7 8 9 10 11 "Technology: The Avelo Solution". diveavelo.com. Avelo Labs. Archived from the original on 24 November 2021. Retrieved 24 November 2021.
  6. 1 2 3 4 5 6 7 8 9 10 "New Tank Lets Scuba Divers Ditch Their BCD". Scuba Diving. PADI Media. 22 November 2021. Archived from the original on 23 November 2021. Retrieved 24 November 2021.
  7. ↑ This is basic physics.
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